Electrical rectifier



Jan. 9,1940. RHDOWUNG 2,186,781

ELECTRICAL RECTIFIER Filed March 19, 1938 Fly.

INVENTOR P1252450 HDowlz'ny.

HIS ATTORNEY Patented Jan. 9, 1940 PATENT OFFICE ELECTRICAL RECTIFIERPhilip H-Doivling, Forest Hills, Pa., assignor to The Union Switch &Signal Company, Swissvale, Pa., a corporation of PennsylvaniaApplication Mai-ch 19, 1938, Serial No. 196,912 3 Claims. (Cl. 175-366)My invention relates to electrical rectifiers, and particularly toelectrical rectifier-s of the copper oxide type. i

One object of my invention is to improve the rectifying characteristicsof rectifiers of the type described. p

A feature of my invention comprises manufacturing copper oxiderectifiers from copper containing a small amount of another metal, such,for example, as lead.

I shall describe one form of rectifiers embodying my invention, andshall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a view showing in side elevationone form of copper blank ready to be manufactured into a rectifierelement in accordance with my invention. Fig. 2 is a view showing anumber of blanks assembled on a support as they appear. during one stepin the process of manufacture. Fig. 3 is a vertical sectional viewshowing, in anexaggerated form, a rectifier element as it appears inanother step in the process of manufacture. Fig. 4 is a view showing acompleted rectifier element constructed in accordance with my invention.

Similar reference characters refer to similar parts in all four views.

Inthe process of manufacturing copper oxide rectifiers, as. it is nowgenerally practiced, a number of copper blanks, which may, for example,be similar to the blank A shown in Fig. 1,

are first cleaned in any suitable manner as by an acid etch, and theseblanks are then assembled in pairs on a suitable support 13 in themanner shown in Fig. 2 so that the blanks of each pair have theiradjacent faces A in contact. The blanks are then heated in the presenceof air in an electric furnace, the temperature of which is usuallymaintained at about 1860" F. This heating of the blanks causes a layerof red or cuprous oxide to be formed on the blanks,

and is'continued until the cuprous oxide layer is.

of the desired thickness. After a sufficient amount of oxide has beenformed on the copper blanks, these blanks are then transferredimmediately to a secondfurnace which is maintained at a temperature ofapproximately 1050" F., and are allowed. to remain in this latterfurnace only for a sufficient length .of time to permit them to cooldown to the temperature of the second furnace. The oxidized blanks arethen removed from the second furnace and are suddenly cooled or"quenched asby plunging the blanks into cold water or a current of coldair. Eachblank then appears as shown'in Fig.

3 from which it will be seen that each blank A is now covered with aninner coating D of cuprous or red oxide of copper and a thin outercoating C of black oxide of copper. It will also be seen from aninspection of Fig. 3 that the 5 flat face A of the blank which isexposed during the oxidizing process, that is to say, the lower face,has a much heavier oxide coating than the upper face. Each blank is nexttreated to remove the black oxide from the lower face of the blank, andboth the black and red oxide from the upper face, after whichthe blankwill appear as shown in Fig. 4. One process which is particularlysuitable for. removing the excess oxide from the blanks is described andclaimed in Letl5 ters Patent of the United States No. 2,094,642 grantedto me on October 5 1937. As a last step, the electrical contact to theexposed face of the cuprous oxide remaining on the blank is improved, asby rubbing into the face powdered petroleum coke.

Rectifier elements of the type described exhibit the characteristic ofoffering a relatively low resistance to current flowing through theelement from the cuprous oxide to the copper and a relatively highresistance to the fiow of current through the element in the oppositedirection. The resistance of the element in the low resistance directionwill hereinafter be referred to as the conducting resistance, while the80 resistance of the element in the high resistance direction willhereinafter be referred to as the blocking resistance.

Rectifier elements of the type described also exhibit the characteristicthat when a voltage is applied to them in the high resistance orblocking direction, the high or blocking resistance will de-. crease atfirst relatively rapidly and then somewhat more slowly with time untilit obtains an apparently stable value which may be consider- 40 ablyless than the initial value. The stable virtual value of the reversecurrent when an alternating voltage is applied to the rectifier isincreased due to this effect, and this effect accordingly insome-instances determines the voltage for which the rectifier is capableof effecting satisfactory' rectification in service. This change inblocking resistance with time is ordinarily known as creep, or reversecreep, and is usually temporary in character, the apparent resistance inthe reverse direction gradually returning toward its original value whenthe voltage'is removed.

I have found that when rectifier elements are manufactured by theprocess previously described, the presence in the copper from which theelements are manufactured or certain metallic impurities appears tomaterially affect the characteristics of the rectifier elements. One

such impurity which I have found to be particularly eflfective inaffecting the characteristics of the elements is lead, the presence ofwhich in proper amounts increases the reverse resistance, decreases thetendency to creep, and also decreases the aging of the rectiflers in theblocking direction. The lead to be effective should be present in aconcentration of at least .001% by weight, and a concentration of 005%by weight gives particularly good results. In certain applications whereexceptional reverse current sta-. bility is of more importance than alow resistance in the conducting direction, concentrations above .005%by weight may at times be found to be useful. In no event, however,should the concentration of the lead be large enough to interfere withthe melting and rolling process by which the sheets or strips from whichthe blanks are punched are formed, nor should it be so large as tointerfere with the adherence of the 'oxide layer 5 'to the mother metal.

One advantage of the use of a copper body containing lead for themanufacture of rectifier elements is that it reduces the detrimentaleffects on the blocking resistance of the presence of anodic impuritiesduring the manufacturing process.

Although I have herein shown and described only one form of electricalrectiflers embodying my invention, it is understood that various changesand modifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. A copper oxide rectifier formed from a copper body containingapproximately .001% by weight lead.

2. A copper oxide rectifier formed from a copper body containingapproximately .005% by weight lead.

3. A copper oxide rectifier formed from a copper body containing between.001% and .005% by weight lead.

PHILIP H. BOWLING.

